The answer to 'how to fix drain cleaning' is to use a plunger or a drain snake to unclog a blocked drain. Start by using a plunger to try and dislodge the clog. If that doesn't work, use a drain snake (also called a plumber's snake or auger) to reach deeper into the drain and break up the blockage. Be sure to wear gloves and eye protection when using these tools.
If the clog is still not cleared, you may need to disassemble the drain pipe to access the blockage. This is a more involved process and it's generally best to call a professional plumber if you're not comfortable doing it yourself. Regular drain cleaning maintenance, such as using a drain cleaner or baking soda and vinegar, can also help prevent future clogs.